1. Field of the Invention
The present invention relates to a piezooscillator provided with a piezoelectric vibrator and configured to stabilize frequency oscillated by the piezoelectric vibrator against a change in ambient temperature using a heating element.
2. Description of the Related Art
As an example of the piezooscillator provided with the piezoelectric vibrator, there is a quartz oscillator provided with a quartz vibrator, and as typical configurations to obtain frequency stability against the temperature of the crystal oscillator, there are known a TCXO (Temperature Compensated Crystal Oscillator) and an OCXO (Oven Controlled Crystal Oscillator) (Nonpatent document 1). The TCXO is configured to have a built-in temperature compensation circuit employing a temperature sensitive element so that the oscillation frequency is corrected based on the value of the temperature detected by the temperature sensitive element. This TCXO has advantages of lower power consumption as compared to the OCXO, and smaller size and weight in general. As compared to OCXO, however, the TCXO is easily affected by the ambient temperature and hence difficult to apply when high frequency stability is required.
Meanwhile, as for the OCXO, the quartz vibrator is enclosed in an oven, and the inside of the oven becomes a constant temperature by being warmed by the heating element such as a heater so that the ambient temperature of the quartz vibrator is kept constant. The description will be given of the configuration in more detail with reference to FIGS. 15A, 15B, 15C. In the drawings, “11” denotes a substrate that is fixed to a substrate 16 via support posts 15 being lead pins while it is in a floating state from the substrate 16. Although it is omitted to show in the drawings to avoid complication, the support posts 15 are connected to the substrate 11 and substrate 16 via solder or the like so that the substrate 11 and substrate 16 are electrically connected. On the substrate 11, a quartz vibrator 12, a heating element 13 and a temperature sensitive element 14 are disposed. In the drawings, “17” is a peripheral circuit including the oscillation circuit, a temperature control circuit and the like. On the substrate 16, a cover 18 is provided to cover the substrate 11, support posts 15 and the peripheral circuit 17, and a space 19 surrounded by the cover 18 and the substrate 16 is configured to be at a constant temperature when the quartz vibrator 12 oscillates. In FIG. 10C, “10” are electrodes provided on a rear surface of the substrate 16.
Note that, as described above, the substrate 11 on which the quartz vibrator 12, heating element 13 and so forth are disposed is provided in the floating state from another substrate 16, this is to reduce power consumption to keep the temperature of the space 19 by suppressing heat dissipation, in that when the substrate 16 is configured to have quartz vibrator 12 and heating element 13 directly disposed thereon, the heat from the heating element 13 is transmitted to the substrate 16 to easily be released outside the OCXO.
With the configuration as described above, the OCXOs are difficult to be affected by the ambient temperature and exhibit an advantage of higher frequency stability, so that they are being employed in mobile communication equipment, transmission communication equipment and so forth; however, in recent years, along with the downsizing of such equipment, the OCXOs are demanded to reduce their size and height. However, the OCXO of the configuration shown in FIG. 15 is configured such that the substrate 11 is floated above the substrate 16 via the support posts 15 and the quartz vibrator 12 is provided on the substrate 11. It is therefore difficult to realize the downsizing and height reduction of the OCXO and, therefore, the OCXO has a height, for example, of approximately 7 mm to 10 mm at minimum.
Further, in order to have the above-described configuration, when manufacturing the OCXO, it is required that the substrate 11 and the quartz vibrator 12 be electrically connected, and the substrate 11 and the substrate 16 be electrically connected. Accordingly, due to an addition of a soldering step or the like, the production process of the OCXO becomes complicated and production cost increase is caused, being problems. Further, the heat of the heating element 13 is released to the substrate 11, causing a problem of increasing power consumption to keep the quartz vibrator 12 be at a preset temperature. Therefore, improvements of these problems have been desired.
(Nonpatent document 1)
Suisho Device no Kaisetsu to Oyo (Description and Application of Quartz Crystal Devices), Quartz Crystal Industry Association of Japan, 18-20 p, March, 2002.